1. Field of the Invention
The present invention relates to a cell driving type piezoelectric/electrostrictive actuator having cells each being defined by wall portions, and capable of achieving a predetermined function due to the volume change of the cell(s) by displacement caused by a piezoelectric operation portion provided on the wall portions.
2. Description of the Related Art
It has passed a long time since an ink jet head was employed for a printer, facsimile machine, copying machine, and other printing apparatuses. In recent years, a non-impact system has been used especially in most of compact size printers, and a clear image has been reproduced on paper by the sophisticated ink let head as in a photograph.
A printing apparatus of the non-impact system means an apparatus for discharging an ink via a nozzle to print some images and/or characters to be printed on a printing medium such as paper. They are classified mainly into a piezoelectric system and a thermal jet system (Bubble Jet (registered trademark), etc.), depending upon type of the ink jet printing head discharging an ink. In these systems, the piezoelectric system denotes a printing apparatus in which a piezoelectric/electrostrictive actuator is used as an ink jet printing head. This ink jet printing head mainly comprises a nozzle, an ink chamber communicating with an ink supply path, and a piezoelectric/electrostrictive device causing a volume change in the ink chamber. In the printing apparatus of the piezoelectric system, the ink jet printing head carries out typing or printing by causing the volume change in the ink chamber while applying a driving voltage to the piezoelectric/electrostrictive device to discharge an ink from the nozzle. Since the ink jet printing head of the piezoelectric system is not required to heat the ink as in the thermal jet system, this type of the printing head has such advantages that freedom in selection of the ink is high, and that the controllability of the printing performance is excellent.
An ink jet (recording) has been disclosed, for example, in Japanese Patent No. 3217006 specification. As shown in FIG. 1 of Japanese Patent No. 3217006 specification, in the proposed ink jet printing head, an electrode coated with a protector film is disposed on the inner surface of a piezoelectric/electrostrictive substrate (plate) to form a groove covered with a lid (top plate) on an upper side. An ink chamber (ink channel) charged with the ink or a dummy chamber (dummy channel) in which any ink is not charged is formed every other groove, and a nozzle plate having a nozzle communicating with the ink chamber is disposed. Opposite side walls of a piezoelectric/electrostrictive body defining the ink chamber (piezoelectric/electrostrictive device in which the electrode is formed) are displaced and deformed to discharge the ink from the nozzle in the ink jet printing head. In the ink jet printing head, the lid has a slit extending through the nozzle plate above the dummy chamber, a depth of the dummy chamber is larger than that of the ink chamber, and the dummy chamber has a depth to such an extent that slip deformation of a bottom part of the dummy chamber is not caused by the deformation of the piezoelectric/electrostrictive side walls constituting the ink chamber. Therefore, crosstalk is reduced, and a stable discharge operation of ink droplets is realized.
However, the above-described conventional ink jet printing heads have been supposed to have several problems. When a conductive liquid is used as an ink in the ink jet printing head, it is indispensable to form the protector film in order to insulate the electrode. Furthermore, depending on a driving polarity, it is necessary to form the protector film in order to prevent electrolysis of the ink regardless of whether or not the ink has conductivity. In the ink jet printing head described in Japanese Patent Registration No. 3217006, after the protector film is formed, the top plate formed of polyimide or the like is bonded with an adhesive. Therefore, when the deformations of the side walls are repeated in a long-term operation, there is a possibility that bonding reliability between the side walls and the top plate drops. Moreover, there is also a possibility that bubbles remain in the ink chamber and discharging defects are caused.
On the other hand when a gap is generated between the side walls and the top plate, the ink remains, and a printing quality drops. In extreme cases, there is a possibility that ink leakage is caused. When the function of the protector film is degraded, there is a possibility that problems such as short circuit and migration occur. The ink jet printing head has been demanded to have a long-period reliability, and it is desirable to thoroughly remove elements resulting in the problems.